This invention relates generally to the charging of storage batteries utilized as a standby source of electrical energy for operation of AC loads normally supplied from an available source of AC voltage.
Storage batteries interconnected in series to establish a bank of batteries between end terminals of opposite polarity are generally well known for supply of electrical energy at a relatively high voltage, such as 120 VDC. Charging of such bank of batteries is ordinarily effected from an AC source, such as a three wire, 60 cycle output of an electrical generator through voltage converters including full wave rectifiers and power coupling transformers. The charging current to the batteries is usually controlled or regulated through the secondary winding of the transformers to maintain the batteries in a fully charged state. The full standby voltage of the bank of batteries when manually switched on to one or more AC loads, must be converted from DC to AC. The use of voltage inverters controlled by firing circuits for such purposes is already well known.
However, the charging of the aforementioned storage battery banks in accordance with prior art charging systems is not completely satisfactory in many loading installations. For example, abrupt changes in load caused either unexpectedly or deliberately by manual switching will sometimes cause damage, from high transients, to either the AC loads, the charging circuit or both. Also, the batteries may not be reliably maintained in a fully charged state and proper operation of the AC loads may not therefore be assured when supplied by energy from the batteries.
It is therefore an important object of the present invention to provide a charging system for a bank of storage batteries which will be maintained in a fully charged state while current is continuously drawn therefrom under varying load conditions imposed on the system dependent either on the AC loads themselves, the AC source to which the loads are connected, or both.
An additional object in accordance with the foregoing object is to more efficiently maintain full charge on the batteries by control over the distribution of current for battery charging and load operating purposes.